Formation of epitaxial layers via dislocation filtering

ABSTRACT

A process for forming a thick defect-free epitaxial layer is disclosed. The process may comprise forming a buffer layer and a sacrificial layer prior to forming the thick defect-free epitaxial layer. The sacrificial layer and the thick defect-free epitaxial layer may be formed of the same material and at the same process conditions.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

The present disclosure claims the benefit of U.S. Provisional Patent Application No. 62/355,787, filed on Jun. 28, 2016 and entitled “Formation of Epitaxial Layers Via Dislocation Filtering,” which is incorporated herein by reference.

FIELD OF INVENTION

The invention relates to processes for forming epitaxial films. Specifically, the invention relates to processes for forming epitaxial layers involving dislocation filtering. More specifically, the processes form germanium-tin and silicon-germanium-tin epitaxial layers.

BACKGROUND OF THE DISCLOSURE

Germanium-tin and silicon-germanium-tin layers have great applicability for optoelectronic applications. In particular, thick strain-free layers may be desired in various optoelectronic device architectures. Growth on lattice-mismatched substrates necessitates strain relaxation via dislocation formation in these layers. However, electronic and optical properties of the epitaxial layer are degraded by the presence of dislocations. As a result, a technique that allows for formation of a thick and dislocation-free epitaxial layer is desired.

SUMMARY OF THE DISCLOSURE

In at least one embodiment of the invention, a process is disclosed. The process may be for forming an epitaxial film on a substrate and comprise: providing a reaction chamber, the reaction chamber holding a substrate to be processed; forming a buffer layer on the substrate; forming a sacrificial layer on top of the buffer layer, wherein the sacrificial layer comprises at least one of: germanium-tin or silicon-germanium-tin; and forming a bulk layer on top of the sacrificial layer, wherein the bulk layer comprises a same material as the sacrificial layer; wherein the sacrificial layer comprises at least one dislocation caused by an interfacial strain; and wherein the bulk layer is substantially free from dislocations caused by an interfacial strain.

For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught or suggested herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments will become readily apparent to those skilled in the art from the following detailed description of certain embodiments having reference to the attached figures, the invention not being limited to any particular embodiment(s) disclosed.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

These and other features, aspects, and advantages of the invention disclosed herein are described below with reference to the drawings of certain embodiments, which are intended to illustrate and not to limit the invention.

FIG. 1 is a cross-sectional view of a semiconductor structure formed in accordance with at least one embodiment of the invention.

FIG. 2 is a flowchart in accordance with at least one embodiment of the invention.

FIG. 3 is a cross-sectional view of a semiconductor structure formed in accordance with at least one embodiment of the invention.

FIG. 4 is a flowchart in accordance with at least one embodiment of the invention.

FIG. 5 is a cross-sectional view of a semiconductor structure formed in accordance with at least one embodiment of the invention.

It will be appreciated that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of illustrated embodiments of the present disclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Although certain embodiments and examples are disclosed below, it will be understood by those in the art that the invention extends beyond the specifically disclosed embodiments and/or uses of the invention and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the invention disclosed should not be limited by the particular disclosed embodiments described below.

Germanium-tin and silicon-germanium-tin layers can be grown epitaxially. Approaches to grow these films are disclosed in U.S. patent application Ser. No. 14/827,177, entitled “Methods of Forming Highly p-Type Doped Germanium Tin Films and Structures and Devices Including the Films,” and U.S. patent application Ser. No. 14/956,115, entitled “Methods of Forming Silicon Germanium Tin Films and Structures and Devices Including the Films,” both of which are incorporated by reference.

However, during formation of the germanium-tin and silicon-germanium-tin films, dislocations may be formed and propagate throughout the layer. These propagated dislocations may adversely affect the operability of the layers in optoelectronic applications.

In accordance with at least one embodiment of the invention, formation of the films may take place in a reaction system used for epitaxial chemical vapor deposition (CVD) processing, such as an Epsilon® 2000 Plus, Epsilon® 3200, or Intrepid XP, manufactured by ASM International N.V., for example. The reaction system may include direct plasma, and/or remote plasma apparatus and/or various heating systems, such as radiant, inductive, and/or resistive heating systems.

FIG. 1 illustrates a semiconductor structure 100 formed in accordance with at least one embodiment of the invention. The semiconductor structure 100 may comprise a substrate 110, a buffer layer 120, a sacrificial layer 130, and a bulk layer 140. The substrate 110 may be comprised of a bulk Si wafer, bulk Ge wafer, or even wafers made III-V semiconductor materials.

The buffer layer 120 may be deposited on top of the substrate 110. The buffer layer 120 may comprise germanium or silicon-germanium-tin (SiGeSn). A buffer layer 120 comprising germanium or SiGeSn may be grown to a thickness of approximately 0.5 μm to 1.5 μm.

The sacrificial layer 130 may be deposited on top of the buffer layer 120. The sacrificial layer 130 may comprise germanium-tin or silicon-germanium-tin. The sacrificial layer 130 may be grown to a thickness ranging between 1 and 10 nm, 20 and 100 nm, or 100 and 200 nm. The sacrificial layer 130 may have a lattice constant that is larger than that of the buffer layer 120 but smaller than or equal to that of the bulk layer 140.

The sacrificial layer 130 may be highly defective and may not provide utility to optoelectronic applications. The dislocations may be due to interfacial strain energy as a result of lattice mismatch. For example, an increased temperature and pressure may result in the formation of the dislocations. The sacrificial layer 130 may have a percentage of tin ranging between 0.5 and 5 at %, 5 and 10 at %, or 10 and 15 at %.

The bulk layer 140 may be deposited on top of the sacrificial layer 130. The bulk layer 140 may comprise the same material as the sacrificial layer 130, either germanium-tin or silicon-germanium-tin. The bulk layer 140 may be grown to a thickness ranging between 100 and 300 nm, 300 and 1000 nm, or 1000 and 2000 nm. The bulk layer 140 may have a lattice constant greater than or equal to that of the sacrificial layer 130.

The bulk layer 140 may differ from the sacrificial layer 130, as the bulk layer 140 may not have the dislocations of the sacrificial layer 130. This may be possible even though the bulk layer 140 is grown at the same process conditions as those of the sacrificial layer 130. As the sacrificial layer 130 reaches a critical thickness during growth, it becomes strain relaxed. The strain relaxation of the sacrificial layer 130 allows increased Sn-incorporation during subsequent growth such that two distinct layers are formed. The nature of the defects in the sacrificial layer may inhibit further propagation into the bulk layer. In addition, the bulk layer 140 may have a percentage of tin ranging between 0.5 and 5 at %, 5 and 10 at %, or 10 and 15 at %, which may be higher than that of the sacrificial layer 130.

FIG. 2 illustrates a method 200 for manufacturing a semiconductor device in accordance with at least one embodiment of the invention. The process may comprise providing a reaction system and a substrate to be processed in the reaction system. The process may also comprise a buffer layer formation step 210, a sacrificial layer formation step 220, and a bulk layer formation step 230.

The buffer layer formation step 210 may comprise a flow of a precursor gas including at least one of: germane (GeH₄) or digermane (Ge₂H₆). A pressure of the reaction chamber during the buffer layer formation step 210 may range between 5 and 20 Torr, 20 and 100 Torr, or 100 and 760 Torr. A temperature of the reaction chamber during the buffer layer formation step 210 may range between 300 and 400° C., 400 and 600° C., or 600 and 850° C.

The sacrificial layer formation step 220 may comprise a flow of a silicon precursor gas, a germanium precursor gas, and a tin precursor gas. The silicon precursor gas may comprise at least one of: silane, disilane, trisilane, tetrasilane, neopentasilane, or other higher order silanes. The silicon precursor gas may also comprise one or more dopant compounds, such as those used to fabricate photonic and/or semiconductor devices, such as diborane, phosphine, or arsine. The germanium precursor gas may comprise at least one of: germane or higher order germanes. The germanium precursor gas may also comprise one or more dopant compounds, such as those used to fabricate photonic and/or semiconductor devices, such as diborane, phosphine, or arsine.

The tin precursor gas may comprise tin chloride (SnCl₄), deuterated stannane (SnD₄), and methyl and/or halide substituted stannanes, such as compounds having a formula Sn(CH₃)_(4-n)X_(n), in which X is H, D (deuterium), Cl, or Br and n is 0, 1, 2, or 3; ZSn(CH₃)_(3-n)X_(n) in which Z is H or D, X is Cl or Br, and n is 0, 1, or 2; Z₂Sn(CH₃)_(2-n)X_(n) in which Z is H or D, X is Cl or Br, and n is 0 or 1; or SnBr₄. Some exemplary tin precursors suitable for use with the present disclosure are discussed in more detail in U.S. application Ser. No. 13/783,762, filed Mar. 4, 2013, entitled “TIN PRECURSORS FOR VAPOR DEPOSITION AND DEPOSITION PROCESSES,” the contents of which are hereby incorporated herein by reference, to the extent such contents do not conflict with the present disclosure.

A pressure of the reaction chamber during the sacrificial layer formation step 220 may range between 500 and 800 Torr, 600 and 780 Torr, or 700 and 760 Torr. A temperature of the reaction chamber during the sacrificial layer formation step 220 may range between 200 and 500° C., 275 and 475° C., or 300 and 420° C.

The bulk layer formation step 230 may comprise flow of the same precursor gases as those in sacrificial layer formation step 220. In addition, a pressure of the reaction chamber during the bulk layer formation step 230 may range between 500 and 800 Torr, 600 and 780 Torr, or 700 and 760 Torr. A temperature of the reaction chamber during the bulk layer formation step 230 may range between 200 and 500° C., 275 and 475° C., or 300 and 420° C.

FIG. 3 illustrates a semiconductor structure 300 formed in accordance with at least one embodiment of the invention. The semiconductor structure 300 may comprise a substrate 310, a buffer layer 320, a dislocation filtering layer(s) 330, and a bulk layer(s) 340. The substrate 310 may comprise a bulk Si wafer, bulk Ge wafer, or even wafers made III-V semiconductor materials.

The buffer layer 320 may be deposited on top of the substrate 310. The buffer layer 320 may comprise germanium or SiGeSn. A buffer layer 320 comprising germanium may be grown to a thickness of approximately 0.5 μm to 1.5 μm.

In this embodiment, alternating layers consisting of the layer bulk composition and the dislocation filtering layer composition are deposited on the buffer layer. The dislocation filtering layer(s) 330 may comprise germanium-tin or silicon-germanium-tin. The layer(s) 330 may be grown to a thickness ranging between 1 and 10 nm, 10 and 20 nm, or 30 and 40 nm. The filtering layers may have lattice constants that are smaller or larger than the lattice constants of the bulk layer or layers.

Initial epitaxial growth of the bulk layer(s) 340 may be highly defective. The filtering layers or layers 330 may be inserted into the growing bulk layer 340 in an alternating architecture to block dislocations from propagating toward the terminal bulk layer, which is the layer of interest for electronic and optoelectronic device applications.

The bulk layer(s) 340 may be deposited on top of the filtering layer(s) 330. The bulk layer 340 may comprise the same material as the sacrificial layer 330, either germanium-tin or silicon-germanium-tin. The bulk layer 340 may be grown to a thickness ranging between 1 and 10 nm, 10 and 20 nm, or 20 and 30 nm. The bulk layers 340 may have lattice constants which are smaller or larger than the lattice constants of the filtering layer or layers.

A sandwich structure of the sacrificial layer 330 and the bulk layer 340 may be formed by repeating the formation of these layers. The sacrificial layers 330 may serve as dislocations filters relative to a thick active layer comprising a plurality of the bulk layers 340.

FIG. 4 illustrates a method 400 for manufacturing a semiconductor device in accordance with at least one embodiment of the invention. The method 400 may comprise providing a reaction system and a substrate to be processed in the reaction system. The method 400 may also comprise a buffer layer formation step 410, a dislocation filtering layer formation step 420, a bulk layer formation step 430, and a repeat loop 440.

The buffer layer formation step 410 may comprise a flow of a precursor gas including at least one of: germane or digermane. A pressure of the reaction chamber during the buffer layer formation step 410 may range between 5 and 20 Torr, 20 and 100 Torr, or 100 and 760 Torr. A temperature of the reaction chamber during the buffer layer formation step 410 may range between 300 and 400° C., 400 and 600° C., or 600 and 850° C.

The dislocation filtering layer formation step 420 may comprise a flow of a silicon precursor gas, a germanium precursor gas, and a tin precursor gas. The silicon precursor gas may comprise at least one of: silane, disilane, trisilane, tetrasilane, neopentasilane, or other higher order silanes. The silicon precursor gas may also comprise one or more dopant compounds, such as those used to fabricate photonic and/or semiconductor devices, such as diborane, phosphine, or arsine. The germanium precursor gas may comprise at least one of: germane or higher order germanes. The germanium precursor gas may also comprise one or more dopant compounds, such as those used to fabricate photonic and/or semiconductor devices, such as diborane, phosphine, or arsine.

The tin precursor gas may comprise tin chloride (SnCl₄), deuterated stannane (SnD₄), and methyl and/or halide substituted stannanes, such as compounds having a formula Sn(CH₃)_(4-n)X_(n), in which X is H, D (deuterium), Cl, or Br and n is 0, 1, 2, or 3; ZSn(CH₃)_(3-n)X_(n) in which Z is H or D, X is Cl or Br, and n is 0, 1, or 2; Z₂Sn(CH₃)_(2-n)X_(n) in which Z is H or D, X is Cl or Br, and n is 0 or 1; or SnBr₄. Some exemplary tin precursors suitable for use with the present disclosure are discussed in more detail in U.S. application Ser. No. 13/783,762, filed Mar. 4, 2013, entitled “TIN PRECURSORS FOR VAPOR DEPOSITION AND DEPOSITION PROCESSES,” the contents of which are hereby incorporated herein by reference, to the extent such contents do not conflict with the present disclosure.

A pressure of the reaction chamber during the dislocation filtering layer formation step 420 may range between 500 and 800 Torr, 600 and 780 Torr, or 700 and 760 Torr. A temperature of the reaction chamber during the dislocation filtering layer formation step 420 may range between 200 and 500° C., 275 and 475° C., or 300 and 420° C.

The bulk layer formation step 430 may comprise flow of the same precursor gases as those in the dislocation filtering layer formation step 420. However, the conditions within the reaction chamber may differ between the two steps in order to form the different layers. For example, a pressure of the reaction chamber during the bulk layer formation step 430 may range between 500 and 800 Torr, 600 and 780 Torr, or 700 and 760 Torr. A temperature of the reaction chamber during the bulk layer formation step 430 may range between 200 and 500° C., 275 and 475° C., or 300 and 420° C. The sandwich structure of the bulk layer and the dislocation filtering layer may be achieved through the repeat loop 440.

FIG. 5 illustrates a semiconductor structure 500 formed in accordance with at least one embodiment of the invention. The semiconductor structure 500 may comprise a substrate 510, a buffer layer 520, a defective intermediate layer 530, and a bulk layer 540. The substrate 510 may comprise a bulk Si wafer, bulk Ge wafer, or even wafers made III-V semiconductor materials.

The buffer layer 520 may comprise a Ge buffer layer. The buffer layer 520 may be a strain-relaxed layer with a low density of threading dislocations.

The defective intermediate layer 530 may comprise GeSn. The defective intermediate layer 530 may be characterized by threading dislocations that may result from a lattice mismatch between the buffer layer 520 and the bulk layer 540. The defective intermediate layer 530 may be a thinner layer in comparison to the buffer layer 520 or the bulk layer 540. The defective intermediate layer 530 has dislocations pinned within the layer 530.

The bulk layer 540 may comprise a GeSn layer that is relatively defect-free. The bulk layer 540 may be strain relaxed due to the dislocations pinned in the defective intermediate layer 530.

It is to be understood that the configurations and/or approaches described herein are exemplary in nature, and that these specific embodiments or examples are not to be considered in a limiting sense, because numerous variations are possible. The specific routines or methods described herein may represent one or more of any number of processing strategies. Thus, the various acts illustrated may be performed in the sequence illustrated, in other sequences, or omitted in some cases.

The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various processes, systems, and configurations, and other features, functions, acts, and/or properties disclosed herein, as well as any and all equivalents thereof. 

What is claimed is:
 1. A process for forming an epitaxial film on a substrate, comprising: providing a reaction chamber, the reaction chamber enclosing a substrate to be processed; forming a buffer layer on the substrate; forming a sacrificial layer on top of the buffer layer; and forming a bulk layer on top of the sacrificial layer, wherein the bulk layer comprises at least one of germanium-tin or silicon-germanium-tin; wherein the sacrificial layer comprises at least one dislocation caused by an interfacial strain; wherein the bulk layer is substantially free from dislocations caused by an interfacial strain; and wherein the bulk layer and the sacrificial layer comprise the same material having the same chemical formula.
 2. The process of claim 1, wherein the forming the sacrificial layer and the forming the bulk layer are alternately repeated.
 3. The process of claim 1, wherein the bulk layer has a percentage of tin ranging between 0.5 and 15 at %.
 4. The process of claim 1, wherein the sacrificial layer has a percentage of tin ranging between 0.5 and 15 at %.
 5. The process of claim 1, wherein the substrate comprises at least one of: a bulk silicon wafer; a bulk germanium wafer; or a wafer made of III-V semiconductor material.
 6. The process of claim 1, wherein the at least one dislocation in the sacrificial layer is caused by an interfacial strain energy from a lattice mismatch.
 7. The process of claim 1, wherein the forming the buffer layer comprises flowing a precursor gas including at least one of: germane or digermane.
 8. The process of claim 7, wherein a pressure of the reaction chamber during the forming the buffer layer ranges between 5 and 760 Torr; and wherein a temperature of the reaction chamber during the forming the buffer layer ranges between 300 and 850° C.
 9. The process of claim 1, wherein the forming the sacrificial layer comprises: flowing a silicon precursor gas; flowing a germanium precursor gas; and flowing a tin precursor gas.
 10. The process of claim 9, wherein the silicon precursor gas comprises at least one of: silane; disilane; trisilane; tetrasilane; neopentasilane; or other higher order silanes.
 11. The process of claim 9, wherein the germanium precursor gas comprises at least one of: germane; or higher order germanes.
 12. The process of claim 9, wherein the tin precursor gas comprises at least one of: tin chloride (SnCl₄), deuterated stannane (SnD₄), and a methyl and/or halide substituted stannane, wherein the methyl and/or halide substituted stannane comprises a compound having a formula represented by at least one of Sn(CH₃)_(4-n)X_(n), in which X is H, D (deuterium), Cl, or Br and n is 0, 1, 2, or 3; ZSn(CH₃)_(3-n)X_(n) in which Z is H or D, X is Cl or Br, and n is 0, 1, or 2; Z₂Sn(CH₃)_(2-n)X_(n) in which Z is H or D, X is Cl or Br, and n is 0 or 1; or SnBr₄.
 13. The process of claim 9, wherein a pressure of the reaction chamber during the forming the sacrificial layer ranges between 500 and 800 Torr; and wherein a temperature of the reaction chamber during the forming the sacrificial layer ranges between 200 and 500° C.
 14. The process of claim 1, wherein the forming the bulk layer comprises flowing a precursor gas including at least one of: germane or digermane.
 15. The process of claim 14, wherein a pressure of the reaction chamber during the forming the bulk layer ranges between 500 and 800 Torr; and wherein a temperature of the reaction chamber during the forming the bulk layer ranges between 200 and 500° C.
 16. A process for forming an epitaxial film on a substrate, comprising: providing a reaction chamber, the reaction chamber enclosing a substrate to be processed; forming a buffer layer on the substrate; forming a first dislocation filtering layer on top of the buffer layer; forming a first bulk layer comprising at least one of germanium-tin or silicon-germanium-tin on top of the first dislocation filtering layer; forming a second dislocation filtering layer on top of the first bulk layer; and forming a second bulk layer on top of the second dislocation filtering layer; wherein the first dislocation filtering layer and the second dislocation filtering layer comprise at least one dislocation caused by an interfacial strain; wherein the first bulk layer and the second bulk layer are substantially free from dislocations caused by an interfacial strain; and wherein the first dislocation filtering layer, the first bulk layer, the second dislocation filtering layer, and the second bulk layer all comprise the same material having the same chemical formula. 